Note 7 - Earnings Per Share (Details Textual)	3 Months Ended	9 Months Ended
	Sep. 30, 2016 shares	Sep. 30, 2017 shares	Sep. 30, 2016 shares
Common Class A [Member]
Common Stock to Dividend or Distribution Payable		0.167
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	351,620	91,385	204,170
Common Class A [Member] | Exercise Price Exceeds Market Price [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	156,610		506,250
Common Class B [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		15,231	47,429
Common Class B [Member] | Exercise Price Exceeds Market Price [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	118,830		56,728